The invention is directed to improvements in a hydraulic vehicle brake system having an anti-skid capability.
The prior art in this area includes a vehicle brake system in accordance with FIG. 1 of German Offenlegungsschrift 31 07 963, in which a valve is built into a brake line originating at the master brake cylinder embodied as a one-way valve. This one-way valve can be opened by means of pressure from the master brake cylinder in the direction of at least one wheel brake. A pressure-equalizing bypass in the form of a line that forms a throttle bypasses the one-way valve. This throttling bypass is intended for completely eliminating any residual brake pressures in the wheel brake cylinders once the brake pedal is released, but this is impossible with check valves that are provided for fast evacuation of the wheel brake cylinders. This is because these check valves, for safety reasons, are equipped with closing springs, but they prevent complete evacuation of the wheel brake cylinders. As it is intended to do, the one-way valve installed in the brake line keeps pressure surges, caused by the return pump during anti-skid operation, from affecting the master brake cylinder. This averts brake pedal motions and consequent impacts on the driver's foot. Because all the pressure fluid to be drawn from the wheel brakes during anti-skid operation has to be collected in a high-pressure reservoir, the reservoir is disadvantageously large and heavy and is also expensive.
A further prior art vehicle brake system is known from German Offenlegungsschrift 26 43 860 having return pumps the outlets of which communicate with damper chambers and, via throttles disposed downstream of the damper chambers, with both the master brake cylinder and anti-skid valve assemblies. Providing the damper chambers in combination with the throttles mean that oscillations originating in the return pumps are damped to such an extent that they are no longer disturbing. However, it is disadvantageous that unless the quantities of pressure fluid flowing through the throttles are absorbed by the wheel brakes, they may possibly cause a very disturbing reciprocation of the brake pedal. This might frighten a timid driver and disadvantageously cause him to partially release the brake pedal.